1. Field of the Invention
The invention is related to the storage of the program history of a digital computer in a memory, and particularly to the storage of branchtype instructions in a memory stack of a pipelined system with one or more processors.
2. Discussion of the Background Information
U.S. Pat. No. 4,016,543, issued Apr. 5, 1977 to Franks et al., entitled "Processor Address Recall System, " disclosed a break-point function in connection with the memory stack for storing the addresses of the most recently executed instructions of a digital processor. The system of the Franks et al. patent is implemented by storing the addresses of all of the most recently executed instructions of a processor in a memory stack, and by pushing them down upon the execution of each instruction.
U.S. Pat. No. 4,176,394, issued Nov. 27, 1979 to David Kaminski et al., entitled "Apparatus for Maintaining a History of the Most Recently Executed Instructions in a Digital Computer," was a program history (P-history) system in which only the most recently executed branch-type instructions were stored in a memory stack. The stack was designated as a P-stack and was dedicated to the P-history function. The present invention is directed to a P-history storage system which may be used with a pipelined processor system with one or more pipelined processors without slowing down the operation of any of the processors, and which allows the P-history stack to be maintained in a random access memory (RAM) which may also be utilized for storage for other purposes on a shared basis.